import java.util.Scanner;

public class TestDemo {
    public static void main(String[] args) {
        int i = 0;
        float sum = 0.0f;
        int flag = 1;
        for (i = 1; i <= 100; i++) {
            sum += flag * 1.0f / i;
            flag = -flag;
        }
        System.out.println(sum);
    }
}


/*int i = 0;
int j = 0;
float sum = 0f;
float sum1 = 0.0f;
float sum2 = 0.0f;
        for (i = 1; i <= 100; i += 2) {
sum1 = sum1 + 1.0f / i;
        }
                for (j = 2; j <= 100; j += 2) {
sum2 = sum2 + 1.0f / j;
        }
sum = sum1 - sum2;
        System.out.println(sum);*/
/*
int i = 0;
float sum = 0.0f;
        for (i = 1; i <= 100; i++) {
        if (i % 2 == 0)
sum -= 1.0f / i;
            else
sum += 1.0f / i;
        }
                System.out.println(sum);*/
